The present invention relates to a method and apparatus for ascertaining and indicating the angular position of an unbalance in a rotor, especially for a balancing machine provided with an angular indicator. The invention is especially useful in machines wherein the body to be balanced is rotated by means other than a universal joint shaft, for example, where the rotor to be balanced is driven by belt means or the like.
There are various methods known for ascertaining the angular position of an unbalance and for indicating such an unbalance in balancing machines. For example, it is known to separate the unbalance into two components which are then displayed in a rectangular coordinate system or in an oblique coordinate system. The two components define the angular position of the unbalance in an unequivocal manner. It is also known to display or indicate the unbalance in a polarcoordinate system whereby again an unequivocal angular indication of the unbalance is assured. It is further known to indicate in addition to the size of the unbalance, also the angular position of the unbalance on a further display device, and relative to a fixed reference or null point. In balancing machines in which the unbalance angle is ascertained by stroboscopic means a scale tape is secured to the body to be balanced or a scale disc rotates in synchronism with the body to be balanced, said disc being provided with an angular graduation or scale which is exposed to light flashes as it rotates in order to display the angular location of the unbalance. After the angular position of the unbalance has been ascertained and displayed on a respective indicator it is necessary to transfer the unbalance position back onto the body to be balanced. Stated differently, the body to be balanced must be marked exactly at the location of the unbalance so that a machining or the like may be performed at such location. Such transfer or marking of the body to be balanced is especially easy where the body is provided with a graduated tape around its circumference or where a graduated scale is provided in the balancing machine which scale rotates in synchronism with the body to be balanced. This is, for example, the case in balancing machines in which the body to be balanced is driven by a universal joint shaft. The graduated scale may even be attached directly to the body to be balanced or a marking representing the scale may be part of the body to be balanced. However, with these prior art devvices it is disadvantageous that the members rotating with the body, such as the universal joint shaft driving the body, or a sensing disc secured to the body may influence the accuracy of the balancing. Besides, additional sensing discs are unwieldy or it is necessary to adapt them individually to each type of body to be balanced. In those devices where the unbalance is displayed directly on the body to be balanced by stroboscopic means, it must be taken into account that the angular indication cannot be stored.